When comparing Jam vs Yarn, the Slant community recommends Yarn for most people. In the question“What are the best front-end package managers?”Yarn is ranked 1st while Jam is ranked 6th. The most important reason people chose Yarn is:

One of the most important aspects of Yarn is determinism (predictability). The lock file ensures that the same dependencies will always be installed in the same way and order regardless of the machine for a given repository.

Pro

Provides the best AMD compatibility allowing for better asynchronous loading

Pro

The same results will be yielded every time yarn is run in a repository

One of the most important aspects of Yarn is determinism (predictability). The lock file ensures that the same dependencies will always be installed in the same way and order regardless of the machine for a given repository.

Pro

Can tell you why a package was installed

yarn why <query> can tell you why a package was installed and what other packages depend on it.

Pro

Good network performance

Yarn efficiently queues up requests and avoids request waterfalls in order to maximize network utilization.

Pro

Fully compatible with major Javascript frameworks

The team working on Yarn has made sure that it would work without a hitch with frameworks like React, Angular or Ember, all of which have strained the limits of npm.

Pro

Good documentation

It looks like it has good documentation.

Pro

Built by the community for the community

Even though it's backed by Facebook, Yarn is built as a community project first and foremost. It's completely open source and hosted on Github. It's released under a standard open source client and has its own GitHub organization and set up to work under the same governance model that other successful projects have used in the past, such as Rust and Ember.

All of this means that both existing and new contributors will always work together to improve the product and introduce new features while also keeping in mind suggestions coming from the community.

Pro

Flat Mode

Resolve mismatching versions of dependencies to a single version to avoid creating duplicates.

Pro

Offline mode

If you've installed a package before, you can install it again without any internet connection.

Pro

Security is put at the forefront

Even though it's still in its early stages of development, security is one of the core values on which Yarn is built. It uses checksums to verify the integrity of every package before executing its code. This also helps avoiding errors related to faulty caching or captive portals.

Further steps are also being taken to improve the security of Yarn which will be implemented in the future.

Pro

Multiple registries

Install any package from either npm or Bower and keep your package workflow the same.

Pro

Network resilience

A single request failing won't cause an install to fail. Requests are retried upon failure.

Pro

Backed by Facebook and Google

Was created in a collaboration of Facebook with Exponent, Google and Tilde.

Cons

Con

Forced AMD compatibility means fewer libraries

AMD is currently not as popular as CommonJS modules, which means if a library isn't supported, you'll have to deal with it yourself.